SSI – Simple Sensor Interface protocol

Application layer is the critical measurement of OSI (Open Systems Interconnection) model which is made up of multiple layers. And SSI (Simple Sensor Interface) protocol works as a trouble free communication protocol for application layer.
With SSI usage, data is shifted between computer’s systems or terminals. But this protocol is the result of multiple companies’ joint effort. These corporations are known as: Nokia (multinational communication company) and Vaisala (develops, and markets environmental and industrial measurement products), Suunto company and so on.

SSI Message Makeup

An SSI message is divided into two parts that are known as 2-bytes header portion and an n-bytes payload portion. But header contents are included: address (of one byte length) and a message type (one byte length). But in SSI v1.2 command-based possible values for a message can be described as: command byte: Q,q (0x51,0x71), direction: C-> and description: query. Similarly, command byte: N,n (0x4E,0x6E), direction: <-S and description: discovery reply. But for command byte: Z,z (0x5A,0x7A), direction: C-> and description is reset sensor device.

Moreover, following group of commands is available for use: Q (query), A (query reply), N (discovery reply), G (get sensor configuration), etc. But to interpret the sensor data from time to time, following commands group is used: R (request the sensor data), V (data response) and D (data response along with the status field). Furthermore, data streaming is performed with O (create sensor observer), L (request a sensor listener) and V (data response) commands etc.

Point-to-point Simple Sensor Interface

SSI Point-to-point message sending can be done with SSI UART usage. Such messages are consisting of a header portion (3-byte), payload portion and a non compulsory cyclic redundancy (idleness) check checksum portion. Moreover, the SSI header is made of one start byte, 2-byte message length and a bitwise negation (2-byte) length.

SSI with reference to networking

NanoIP applications for networking and UART are two major users of SSI protocol for the point-to-point system’s communications. Polling and streaming sensor information is possible with it. The decisive factors for Simple Sensor Interface protocol growth are known as: general purpose, minimal overhead and petite server side footprint.

But in an inconsistence environment, nanoIP (nano internet protocol) performs an important role in the SSI networking. The standard of the nano internet protocol (an open-source project) is to put into practice another networking stack in a controlled, automated and sensor network. This protocol (nanoIP) is also offered Internet-like characteristics for example, a socket interface, dependable and undependable framing pattern, ports and fragmentation etc.

However, in different situation SSI in combination with other protocols as nanoUDP can be used as a message format. But in another case, an individual message becomes important if nanoTCP is used in order to provide a flow control etc.

In addition to this, a nanoUDP message is containing different parts that are known as: nanoUDP header (5 bytes), n-bytes message payload and optional CRC checksum (2 bytes). The header is further consisted of a single protocol byte, a 2-bytes message length, and besides this, one byte for source port and one byte for destination port number. Anyhow, destination side port number for SSI message must be 0x28. Different SSI versions can come in front of you which are known as: ver 0.1 in March 14, 2003, ver 0.2 in April 29, 2003, ver 0.3 in May 20, 2003, ver 0.4 in October 2, 2003, ver 0.5 in  December 5, 2003 and so on.



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